Cold-start engine loading for accelerated warming of exhaust aftertreatment system

ABSTRACT

The methods of the present invention are adapted to adjust engine loading during catalyst warm up to accelerate heating of the exhaust aftertreatment system and thereby decrease catalyst light-off times. According to a preferred embodiment of the present invention, the method includes: monitoring the current catalyst temperature; determining if the current catalyst temperature is less than a predetermined minimum catalyst temperature; and, if the current catalyst temperature is less than the predetermined minimum catalyst temperature, increasing the current engine load. The current engine load is increased by activating a reducing agent tank heating device and/or a reducing agent line heating device.

TECHNICAL FIELD

The present invention relates generally to exhaust aftertreatmentsystems. More particularly, the present invention is drawn to methodsfor accelerated warming of motor vehicle exhaust aftertreatment systems.

BACKGROUND OF THE INVENTION

Almost all conventional motorized vehicles, such as the modern-dayautomobile, include an exhaust aftertreatment system for mitigating thebyproducts generated from operation of an internal combustion engine.Most exhaust aftertreatment systems include a catalytic converter forthe reduction and oxidation of exhaust gas emissions, and a mufflerassembly or similar device for attenuating noise generated by theexhaust emission process. The catalytic converter is normally placedbetween the engine exhaust manifold and the muffler of the automobile,but can also be integrated into the muffler assembly.

Catalytic converters normally include a monolith substrate, generally ofthe ceramic honeycomb or stainless steel foil honeycomb type. Themonolith substrate is coated with a catalyst that contains a preciousmetal, such as platinum, palladium, or rhodium. The precious metalfunctions to convert noxious or otherwise environmentally unfriendlycomponents of the exhaust gas, such as hydrocarbons (HC), carbonmonoxide (CO), and nitrogen oxides (NO_(x)), into carbon dioxide (CO₂),water (H₂O) and nitrogen (N). A “washcoat” is frequently employed tomake catalytic converters more efficient. The washcoat, most often amixture of silica and alumina, is added to the substrate, and forms arough, irregular surface which has a far greater surface area than theflat core surfaces. The irregular surface gives the monolith substrate alarger overall surface area, and therefore more locations for activeprecious metal sites.

The NO_(x) emissions from an internal combustion engine, in particular acompression-ignited diesel engine, can also be lowered with the aid ofSelective Catalytic Reduction (SCR). SCR is a means of converting NO_(x)emissions into diatomic nitrogen (N₂) and water (H₂O) using an aqueousreducing agent introduced into the exhaust system, upstream of thehydrolysis catalytic converter. The reducing agent that is used for SCRis typically a gaseous ammonia (NH₃), ammonia in aqueous solution, orurea in aqueous solution. With regard to the latter, urea serves as anammonia carrier and is injected into the exhaust system with the aid ofa metering system. The urea is converted into ammonia by means ofhydrolysis, and the ammonia in turn reduces the nitrogen oxides in thecatalytic converter.

Some emission control devices, such as SCR systems, catalyticconverters, and associated exhaust gas oxygen (EGO) and NO_(x) sensors,require a minimum operating temperature to function as desired. Forexample, one of the limitations to using an aqueous urea solution in SCRis that it is subject to freezing. If the urea solution freezes, it willnot function in its desired manner as a reducing agent, nor will itfreely flow to the reduction site. As such, line heaters are utilized towarm the aqueous urea. In addition, the catalyst coating inside of thecatalytic converter requires a minimum “activation” temperature forefficient operation. As such, a considerable amount of overall tailpipehydrocarbon emissions is generated during engine cold-start. During suchtime, the emissions-reducing catalysts are largely ineffective becausethey have not reached the temperature at which significant catalyticactivity can be maintained, also known as catalytic “light-off”.

SUMMARY OF THE INVENTION

The methods of the present invention are adapted to adjust engineloading during catalyst warm up to accelerate heating of the exhaustaftertreatment system and thereby decrease catalyst light-off times. Inso doing, overall tailpipe nitrogen oxide emissions generated duringengine cold-start are significantly reduced.

According to one embodiment of the present invention, the methodincludes: monitoring the current temperature of the catalyst;determining if the current catalyst temperature is less than apredetermined minimum catalyst temperature; and, if the current catalysttemperature is less than the predetermined minimum catalyst temperature,increasing the current engine load. The current engine load is increasedin accordance with the present invention by activating a reducing agenttank heating device, a reducing agent line heating device, or both.Adjusting the engine load during cold-start using, for example, the ureatank and line heaters will allow for precise calibration of thecatalytic converter warm up cycle.

According to one aspect of this particular embodiment, the method alsoincludes calculating the minimum engine load required to increase thecurrent catalyst temperature to the predetermined minimum catalysttemperature. The current engine load is thus increased to equal theminimum engine load if the current catalyst temperature is less than thepredetermined minimum catalyst temperature.

According to another aspect, the method also includes calculating theminimum alternator load necessary to induce the minimum engine loadrequired to increase the current catalyst temperature to thepredetermined minimum catalyst temperature. In this instance, thereducing agent tank heating device, reducing agent line heating device,or both, are commanded to generate the minimum alternator load. Ideally,the method will then also include calculating the requisite minimumelectric draw of the reducing agent tank heating device and reducingagent line heating device to generate the minimum alternator load.

As part of another aspect of this embodiment, the method also includesdetermining whether the current engine load is less than the minimumengine load. To this regard, the current engine load is increased ifboth the current catalyst temperature is less than the predeterminedminimum catalyst temperature and the current engine load is less thanthe minimum engine load.

In accordance with another aspect, the minimum engine load andpredetermined minimum catalyst temperature parameters are each based, atleast in part, upon the current engine load and speed.

According to yet another aspect, the method adjusts activation of thereducing agent tank heating device and/or reducing agent line heatingdevice in response to variations in vehicle operating conditions (e.g.,changes in vehicle speed, tractive demands, electric system demands,etc.). Adjusting activation of the reducing agent tank heating deviceand/or reducing agent line heating device in this manner allows thesystem to shift engine loading into an optimal zone for catalyst warm-upand light-off.

According to even yet another aspect, the method also includes adjustingengine fuel command to compensate for the increase in engine loadgenerated via activation of the reducing agent tank heatingdevice/reducing agent line heating device.

In accordance with yet another facet of this embodiment, the method alsoincludes: monitoring the current temperature of the exhaust gas;determining whether the current exhaust temperature is less than apredetermined minimum exhaust temperature; and increasing the currentengine load if both the current catalyst temperature is less than thepredetermined minimum catalyst temperature and the current exhausttemperature is less than the predetermined minimum exhaust temperature.

The above features and advantages, and other features and advantages ofthe present invention will be readily apparent from the followingdetailed description of the preferred embodiments and best modes forcarrying out the present invention when taken in connection with theaccompanying drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram or flow chart illustrating a method accordingto a preferred embodiment of the present invention;

FIG. 2 is a graphical illustration of conversion efficiency as afunction of catalyst temperature at various exhaust mass flow rates; and

FIG. 3 is a graphical illustration of catalyst temperature as a functionof engine load at various engine speeds.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, FIG. 1 illustrates a control algorithm forregulating the temperature of an exhaust gas aftertreatment system in amotorized vehicle (not shown). Specifically, an improved method foraccelerated warming of motor vehicle exhaust aftertreatment systems isshown in FIG. 1 in accordance with a preferred embodiment of the presentinvention, designated generally as 100. The method 100 preferablyincludes at least those steps shown in FIG. 1—i.e., steps 101-115.However, it is within the scope and spirit of the present invention toomit steps, include additional steps, and/or modify the order presentedin FIG. 1. It should be further noted that the method 100 represents asingle operation. As such, it is contemplated that the method 100 beapplied in a systematic and repetitive manner, run in real-time tocontinuously adjust engine loading and optimize operation of the exhaustaftertreatment system.

The control algorithm 100 preferably resides in an engine control module(ECM, not shown). In other words, the series of blocks shown in FIG. 1may represent individual steps performed by the ECM. The ECM is aconstituent part of the vehicle's powertrain system, which includes aninternal combustion engine (ICE)—e.g., a 4-stroke compression-igniteddiesel engine or a 4-stroke spark-ignited gasoline engine (neither ofwhich are explicitly depicted herein). The vehicle will also includemany other standard components and systems, such as suspension, drivetrain, brake system, steering and body components, that are also wellknown in the art. Thus, these structures will not be individuallyillustrated or explicitly discussed in detail herein.

The vehicle will also include an exhaust aftertreatment system utilizedto mitigate the byproducts generated from operation of the ICE, androute the exhaust gasses away from the engine for subsequent expulsioninto the ambient atmosphere. The exhaust system includes a number ofexhaust pipes or conduits that fluidly couple a catalytic converterdevice of conventional architecture to an exhaust manifold of the ICE.Other exhaust aftertreatment devices may also be included. For example,a muffler or silencer that is fluidly communicated with a resonator maybe placed downstream from the catalytic converter device via a secondintermediate exhaust pipe.

The exhaust system also includes a Selective Catalytic Reduction (SCR)assembly. The reducing agent used in this exemplary embodiment is anaqueous urea solution, which is stored in a reducing agent storagevessel (also referred to herein as “urea tank”). A metering controlapparatus, which is assigned to the urea tank, has an electricallyactuated pump for delivering the reducing agent to a delivery site(which may be upstream from or directly at the catalytic converterdevice) via a feed line. The metering control apparatus controls anelectromagnetic metering valve which regulates the distribution of ureasolution. An electrical heater device operates to selectively heat theurea tank, for example, during cold-start operation. An electrical lineheater may also be employed to heat the reducing agent as it exits thetank. While the methods of the present invention may be used in anyvehicle having a reducing agent reservoir and corresponding heatingdevice, the present invention is particularly well suited for use with avehicle having a compression-ignited diesel-fueled internal combustionengine (ICE) assembly.

With reference again to FIG. 1, the method starts at step 101 withmonitoring the current temperature of the catalyst inside of thecatalytic converter, which can be accomplished, for example, using aprecious metal resistor-precise thermo couple. In step 103, the methodthen determines whether the current catalyst temperature is below atarget minimum catalyst temperature. The target minimum catalysttemperature may be predefined as a single optimal temperature for alloperating conditions, or determined contemporaneously with step 103using a map of temperatures as a function of the current engine speedand load. For example, FIG. 2 illustrates the relationship betweencatalyst temperature, in degrees Celsius (° C.), and the conversionefficiency of the catalyst (i.e., ratio of NO_(x) entering catalyticconverter versus NO_(x) leaving the catalytic converter) at severalexhaust mass flow rates, provided in kilograms per hour (kg/hr). As canbe seen in FIG. 2, a 250° C. catalyst temperature produces approximatelyan 85% efficiency or better, regardless of mass flow rate. As such, thetarget minimum catalyst temperature may be predefined at 250° C. forthis particular catalytic converter configuration. Alternatively, if a90% or better efficiency is required, the target minimum catalysttemperature may be varied depending upon the exhaust mass flow rate,engine speed, and/or engine load to achieve a 90% efficiency.

If, at step 103, the current catalyst temperature is greater than (i.e.,hotter) or equal to the target minimum catalyst temperature, the controlalgorithm 100 returns to step 101. If, at step 103, the current catalysttemperature is less than (i.e., cooler) the target minimum catalysttemperature, the method 100 proceeds to step 105. In step 105, thecontrol algorithm 100 detects the current engine speed, preferably inrevolutions per minute (rpm), and engine load, preferably inNewton-meters (Nm). According to preferred practice, the engine speedand engine load are monitored continuously throughout execution ofmethod 100.

Contemporaneous with step 105, the minimum engine load required toincrease the current catalyst temperature to the predetermined minimumcatalyst temperature is calculated in step 107. The minimum engine loadparameter is based, at least in part, upon the current engine load andspeed. FIG. 3 of the drawings illustrates the relationship betweencatalyst temperature, in degrees Celsius (° C.), and engine load,preferably in Newton-meters (Nm), at various engine speeds, provided inrevolutions per minute (rpm). By way of example, if the target minimumcatalyst temperature is 250° C. and the engine is idling during vehiclestartup at 800 rpm, the engine load will have to be increased toapproximately 152 Nm to achieve the desired catalyst temperature. If,however, the engine is running at 1000 rpm, the minimum engine loadparameter would be set to approximately 112 Nm to achieve the desired250° C. catalyst temperature.

Prior to, contemporaneous with, or immediately after steps 105 and 107,the current engine load is adjusted to equal or exceed the minimumengine load established above. The current engine load is increased inaccordance with the present invention by activating the urea tank heaterand line heater, either individually or in concert, at step 111. Exhausttemperature generally rises as engine load increases, whereas exhausttemperature generally falls as engine load decreases. To ensure that theurea tank heater and/or line heater generate sufficient additional loadon the engine during activation, the method also includes, in step 109,calculating the minimum alternator load necessary to induce the minimumengine load. This may also require calculating the minimum electric drawof the urea tank heater and/or line heaters necessary to generate theminimum alternator load. In this instance, the method 100 commands thereducing agent tank heater, reducing agent line heating device, or both,to generate the minimum alternator load.

Adjusting the engine load, for example, during cold-start using the ureatank heater and line heaters will accelerate heating of the exhaustaftertreatment system and thereby decrease catalyst light-off times. Thepresent invention also allows for precise calibration of the catalyticconverter warm up cycle. In addition, regulating engine load inaccordance with the present invention is effectively seamless to thevehicle operator, as turning on the urea tank and corresponding heatingelements is an entirely invisible process to an end user.

Prior to step 111, it is desirable that the method 100 determine whetherthe engine is already operating at or above the minimum engine load. Ifthe current engine load is already equal to or greater than the minimumengine load required to achieve the target minimum catalyst temperature,the method 100 returns to step 101. If not, the method 100 will proceed,as described above, to step 111.

With continuing reference to FIG. 1, step 113 of method 100 provides foradjusting the urea tank and line heater activity in response tovariations in vehicle operating conditions. Such operating conditionsmay include, but certainly are not limited to, changes in vehicle speed,tractive demands, electric system demands, etc. Adjusting activation ofthe reducing agent tank and/or reducing agent heating device in thismanner allows the system to shift engine loading into an optimal zonefor catalyst warm up and light-off. Due to the additional loading on theengine, the fuel command may need to be adjusted to offset theadditional demand. Accordingly, in step 115, the method 100 alsoincludes adjusting engine fuel command to compensate for the increase inengine load generated via activation of the reducing agent tank and/orreducing agent heating device.

Prior to completing the control algorithm, it may be desirable tomonitor the current temperature of the exhaust gas, which may beaccomplished, for example, using an electrical exhaust gas temperature(EGT) gauge. Thereafter, the method 100 will determine whether thecurrent exhaust temperature is less than a predetermined minimum exhausttemperature. In this instance, the current engine load is increased ifboth the current catalyst temperature is less than the predeterminedminimum catalyst temperature and the current exhaust temperature is lessthan the predetermined minimum exhaust temperature.

While the best modes for carrying out the present invention have beendescribed in detail herein, those familiar with the art to which thisinvention pertains will recognize various alternative designs andembodiments for practicing the invention within the scope of theappended claims.

1. A method for warming an exhaust aftertreatment system to improveperformance of a catalyst, comprising: monitoring a current catalysttemperature; determining whether the current catalyst temperature isless than a predetermined minimum catalyst temperature; and increasing acurrent engine load if the current catalyst temperature is less than thepredetermined minimum catalyst temperature; wherein increasing thecurrent engine load includes activating at least one of a reducing agenttank heating device and a reducing agent line heating device.
 2. Themethod of claim 1, wherein increasing the current engine load includescalculating a minimum engine load required to increase the currentcatalyst temperature to the predetermined minimum catalyst temperature,and increasing the current engine load to equal the minimum engine load.3. The method of claim 2, wherein increasing the current engine loadfurther includes calculating a minimum alternator load required toinduce the minimum engine load, and commanding the at least one reducingagent tank heating device and reducing agent line heating device togenerate the minimum alternator load.
 4. The method of claim 3, whereinincreasing the current engine load further includes calculating aminimum electric draw of the at least one reducing agent tank heatingdevice and reducing agent line heating device required to generate theminimum alternator load.
 5. The method of claim 2, wherein increasingthe current engine load further includes determining whether the currentengine load is less than the minimum engine load, and increasing thecurrent engine load if the current catalyst temperature is less than thepredetermined minimum catalyst temperature and the current engine loadis less than the minimum engine load.
 6. The method of claim 2, whereinthe minimum engine load is based at least in part upon the currentengine load and a current engine speed.
 7. The method of claim 1,wherein the predetermined minimum catalyst temperature is based at leastin part upon the current engine load and a current engine speed.
 8. Themethod of claim 1, wherein increasing the current engine load furtherincludes adjusting activation of the at least one reducing agent tankheating device and reducing agent line heating device in response tovariations in vehicle operating conditions.
 9. The method of claim 1,further comprising: adjusting a fuel command to compensate for theincrease in engine load.
 10. The method of claim 1, further comprising:monitoring a current exhaust temperature; determining whether thecurrent exhaust temperature is less than a predetermined minimum exhausttemperature; and increasing the current engine load if the currentcatalyst temperature is less than the predetermined minimum catalysttemperature and the current exhaust temperature is less than thepredetermined minimum exhaust temperature.
 11. A method for acceleratedwarming of an exhaust aftertreatment system having a catalytic converterdevice with a catalyst for the reduction and oxidation of emissionsgenerated by an internal combustion engine in a motorized vehicle, themethod comprising: establishing a target minimum catalyst temperature;monitoring a current catalyst temperature; determining whether thecurrent catalyst temperature is less than the target minimum catalysttemperature; calculating a minimum engine load required to increase thecurrent catalyst temperature to the target minimum catalyst temperature;calculating a minimum alternator load required to induce the minimumengine load; increasing a current engine load to equal the minimumengine load if the current catalyst temperature is less than the targetminimum catalyst temperature; wherein increasing the current engine loadincludes activating a reducing agent tank heating device and a reducingagent line heating device, and commanding the reducing agent tankheating device and reducing agent line heating device to generate theminimum alternator load.
 12. The method of claim 11, further comprising:monitoring the current engine load and a current engine speed; whereinestablishing the target minimum catalyst temperature is based at leastin part upon the current engine load and the current engine speed. 13.The method of claim 11, wherein increasing the current engine loadfurther includes calculating a minimum electric draw of the reducingagent tank heating device and reducing agent line heating devicerequired to generate the minimum alternator load.
 13. The method ofclaim 11, wherein increasing the current engine load further includesadjusting activation of the reducing agent tank heating device andreducing agent line heating device in response to variations in vehicleoperating conditions.
 14. The method of claim 11, further comprising:increasing a fuel command to the engine to offset the increase in engineload generated by activating the reducing agent tank and reducing agentheating device.